1,721,073 research outputs found
A particle-mesh algorithm for advection-reaction-diffusion equations with applications to plankton modeling
No full textThe interplay of advection, reaction and diffusion terms in ADR equations is a rather difficult one to be modeled numerically. The kind of spurious oscillations that is usually harmless for non-reacting scalars is often amplified without bounds by reaction terms. Furthermore, in most biogeochimical applications, such as mesoscale or global-scale plankton modeling, the diffusive fluxes may be smaller than the numerical ones.
Inspired by the particle-mesh methods used by cosmologists, we propose to discretize on a grid only the diffusive term of the equation, and solve the advection-reaction terms as ordinary differential equations along the characteristic lines. Diffusion happens by letting the concentration field carried by each particle to relax towards the diffusive field known on the grid, without redistributing the particles.
This method, in the limit of vanishing diffusivity and for a fixed mesh size, recovers the advection-reaction solution with no numerical diffusion. We show some example numerical solutions of the ADR equations stemming from a simple predator-prey model
A Diffusive-Hyperbolic Model for Heat Coduction
No full textThe present paper faces the problem of heat conduction within the framework of
thermodynamics with internal state variables. A model, in which the heat flux vector depends both
on the gradient of the absolute temperature and the gradient of a scalar internal variable, is proposed.
Such a model leads to a diffusive-hyperbolic system which in general is parabolic, but also allows to
shift to the hyperbolic regime. In the hyperbolic case the propagation of weak discontinuity waves is
investigated. The Rankine-Hugoniot and Lax conditions for the propagation of strong shock waves
are analyzed as well
Exploitation of the entropy principle: Proof of Liu theorem if the gradients of the governing equations are considered as constraints
No full textThe exploitation of the entropy principle in thermodynamics with Lagrange multipliers
(the so called Liu procedure) is based on the celebrated Liu theorem. In
some recent papers, where either rigid heat conductors or Korteweg fluids have been
considered, the Liu procedure has been generalized by using the gradients of the
governing equations as additional constraints. Here, a rigorous proof of the validity
of the extended procedure to arbitrary first-order nonlocal continua is provided,
thus explicitly generalizing the Liu theorem. As an application, heat conducting
first-order Korteweg-type fluids with a scalar internal variable are analyzed. The
thermodynamic restrictions are determined by the extended Liu procedure. Moreover,
a comparison with the thermodynamic analysis obtained by the application of
an extended Coleman–Noll procedure is performed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Thermodynamical setting for gradient continuum theories with vectorial internal variables:Application to granular materials
No full textThe exploitation of the entropy principle in thermodynamics with Lagrange multipliers, the so–called
Liu procedure,is based on the celebrated Liu theorem. In some recent papers, the Liu procedure has
been generalized by considering the gradients of the governing equations as additional constraints.
Here, we apply this generalized procedure to the equations of a continuum with vectorial internal
variable and first-order non-loca lstate space. Then, owing to the obtained results, we develop a
thermodynamic model for continua with scalar microstructure
Thermo-electrodynamics of rigid superconductors
No full textThis paper deals with a continuum model of rigid superconductors. It is assumed
that their property of shifting to the superconductive state for suitable values of
temperature and magnetic field is due to a vectorial internal variable, related to the
superelectron current by a linear constitutive law. The compatibility of the model
with the second law of thermodynamics is investigated. The propagation of thermoelectromagnetic
waves through a one-dimensional conductor is analyzed as well. Comparison
is made with different continuum approaches which may be found in the
literature
Rare-earth elements abundance and distribution in pelagic sediments by neutron activation analysis
No full textThe geochemical behavior of REE has been tested in the Umbro-Marchean (Italy) pelagic sequences of Cretaceous-Paleocene age. REE were determined by 1NAA in a number of limestone, marl and clay samples. Both chondrite and shale normalized patterns are discussed: .the observed REE amounts and distributions are mainly attributed to highly complex diagenetic processe
On an Inverse Problem in Group Analysis of PDE's: Lie--Remarkable Equations
No full textWithin the framework of inverse Lie problems we give some nontrivial examples of Lie remarkable equations, i.e., classes of partial differential equations that are in onetoone correspondence with their Lie point symmetries. In particular, we prove that the second order Monge-Ampere equation in two independent variables is Lie remarkable. The same property is shared by some classes of second order Monge-Ampere equations involving more than two independent variables, as well as by some classes of higher order Monge-Ampere equations in two independent variables. In closing, also the minimal surface equation in R^3 is
considered
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